1. Field of the Invention
The invention relates to an amplifier arrangement comprising
a transadmittance circuit having an input coupled to an input of the amplifier arrangement, and PA1 a transimpedance amplifier having an input coupled to an output of the transadmittance circuit and an output coupled to an output of the amplifier arrangement, the transfer function modulus of the transimpedance amplifier having a first-order decrease above a first frequency F1 and a second-order decrease above a second frequency F2, said transimpedance amplifer being negatively fed back by means of a negative current feedback circuit.
2. Description of Related Art
An amplifier of this type used as an instrumentation is known from IEEE Journal of Solid-State Circuits, December 1975, pages 424-431. The negatively fed back transimpedance amplifier shown in FIG. 5 of this Article is constituted by a voltage amplifier whose input is connected to ground by means of an input resistor. A current applied to this input produces a voltage across the input resistor, which voltage is subsequently amplified by the voltage amplifier. The output of the voltage amplifier is coupled to its input by means of a transconductance amplifier which ensures a negative current feedback.
In this known arrangement, the negative current feedback circuit is constituted by a transconductance amplifier having an output resistance which is large as compared with the input resistance of the transimpedance amplifier, which is relatively large anyway in the known transimpedance amplifier. However, a drawback of using a transconductance amplifier is that it should be able to cope with a large voltage swing of the output signal of the transimpedance amplifier as in the case of, for example, a video output amplifier. However, such a transconductance circuit cannot be realized in a simple manner. Another detrimental result of the finite value of the input resistance of the transimpedance amplifier is that, together with parasitic capacitances which are present, it limits the bandwidth of the amplifier arrangement.
Amplifier arrangements having a relatively large bandwidth are required for, for example, high-definition television, color-graphic display devices, computer monitors and digital signal processing of signals sampled at high sampling frequencies. The bandwidth of the known amplifier arrangement is, however, too limited for such uses.